1. Field of the Invention
The present invention relates to a recording tape cartridge which rotatably accommodates a reel on which a recording tape, such as a magnetic tape or the like, is wound.
2. Description of the Related Art
Recording tapes, such as magnetic tapes and the like, are used as external recording media of computers and the like. Little space is required for storage of the recording tape, and a large amount of information can be recorded thereon. A so-called single-reel recording tape cartridge is used which rotatably accommodates, within a case, a single reel on which such a recording tape is wound.
Such a recording tape cartridge has a braking means so that the reel does not rotate within the case when the recording tape cartridge is not being used (see, for example, Japanese Patent No. 3187022). A recording tape cartridge equipped with this braking means will be described hereinafter on the basis of FIGS. 11 and 12.
In a recording tape cartridge 200 shown in FIG. 11, a single reel 204 is accommodated within a case 202. The case 202 has a gear opening 206 which is formed at the central portion of a floor plate 202A of the case 202, and a rotation restricting rib 208 which projects downward from a ceiling plate 202B of the case 202.
The reel 204 has a reel hub 210 which is formed in the shape of a cylinder having a floor, and on whose outer peripheral portion a recording tape is wound. A lower flange 204A extends outwardly in the radial direction, integrally from a vicinity of the bottom end of the reel hub 210. On the other hand, an upper flange 204B is fixed to the top end portion of the reel hub 210 by welding or the like.
A reel gear 214, which can mesh with a driving gear 212A formed at a rotating shaft 212 of a drive device, is formed in an annular form at the bottom surface of a floor portion 210A of the reel hub 210. Through holes 216, which pass through the floor portion 210A, are provided at a plurality of places which are evenly spaced on a circumference at the region where the reel gear 214 is formed. The diameter of each through hole 216 is greater than the gear pitch of the reel gear 214. Teeth of the reel gear 214 are not provided around each through hole 216.
Anchor projections 218 stand erect at the top surface of the floor portion 210A of the reel hub 210, at plural positions (discretely) between the through holes 216 which are disposed along a predetermined circumference. A gear tooth 218A is formed at the top end portion of each anchor projection 218.
A disc-shaped braking member 220 is inserted in the reel hub 210. A braking gear 220A, which is annular and which can mesh with the gear teeth 218A, is provided at the bottom surface of the braking member 220. A projection 222 stands erect at the top surface of the braking member 220. An insertion groove 222A, in which the rotation restricting rib 208 of the case 202 is inserted, is provided at the projection 222. Due to the rotation restricting rib 208 being inserted in the insertion groove 222A, the braking member 220 cannot rotate with respect to the case 202. Further, the braking member 220 can move in the vertical directions while being guided by the rotation restricting rib 208.
A compression coil spring 224 is disposed between the ceiling plate 202B of the case 202 and the braking member 220. Usually, the braking member 220 is urged downward by the urging force of the compression coil spring 224, such that the braking gear 220A meshes with the gear teeth 218A. In this way, there is usually a rotation locked state in which rotation of the reel 204 with respect to the case 202 is impeded. Further, the reel gear 214 is exposed from the gear opening 206 while the reel 204 is pushed against the floor plate 202A of the case 202 by this urging force.
Moreover, a releasing member 226 is disposed between the floor portion 210A of the reel hub 210 and the braking member 220, so as to abut both. The releasing member 226 has leg portions 226A which are formed in the shape of plates which do not interfere with the anchor projections 218, and which enter into the respective through holes 216.
Due to the driving gear 212A meshing with the reel gear 214, as shown in FIG. 12, the leg portions 226A are pushed by the driving gear 212A against the urging force of the compression coil spring 224, and the releasing member 226 is pushed upward. When the braking member 220 is pushed upward while the releasing member 226 moves away from the floor portion 210A, the meshing of the braking gear 220A and the gear teeth 218A is released. At this time, the reel 204 also floats up from the floor plate 202A, and the reel 204 becomes able to rotate within the case 202.
When the rotating shaft 212 rotates, the reel 204, whose reel gear 214 is meshing with the driving gear 212A of the rotating shaft 212, rotates within the case 202. At this time, the releasing member 226 rotates together with the reel 204, and the axially central portion of the releasing member 226 slidingly contacts the axially central portion of the braking member 220. Thus, the axially central portion of the braking member 220 is a convex portion 220B which is formed in the shape of a substantially spherical surface, and substantially point-contacts the axially central portion of the releasing member 226.
On the other hand, when the meshed state of the driving gear 212A and the reel gear 214 is released, due to the urging force of the compression coil spring 224, the braking member 220 moves downward, the braking gear 220A and the gear teeth 218A mesh together, and the reel 204 is pushed against the floor plate 202A. In this way, the reel 204 returns to the rotation locked state in which rotation of the reel 204 with respect to the case 202 is impeded.
In recent years, not only horizontal-type drive devices, in which the recording tape cartridge 200 is loaded such that the axial direction of the reel 204 coincides with the vertical direction, but also vertical-type drive devices, in which the recording tape cartridge 200 is loaded such that the axial direction of the reel 204 coincides with the horizontal direction, have come to be used.
In a vertical-type drive device, there are cases in which the reel 204 moves in the radial direction with respect to the case 202 due to gravity. The applicant of the present application has already filed patent applications (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-343058) which propose, as a countermeasure to this problem, a structure in which the clearance between the inner peripheral portion of the reel hub 210 and the braking member 220, which is supported at the case 202, is made to be small, such that radial direction movement of the reel 204 with respect to the case 202 is restricted via the braking member 220. Specifically, a plurality of standing ribs 228, which oppose the outer peripheral surface of the braking member 220, are formed so as to project along the axial direction at the inner peripheral surface of the reel hub 210.
In this way, the amount of movement of the reel 204 with respect to the case 202 within a vertical-type drive device is restricted, and the reel gear 214 of the reel 204 and the drive gear 212A of the drive device can mesh together appropriately. Note that the reason why the standing ribs 228 are formed to project at the inner peripheral surface of the reel hub 210 is as follows: the upper flange 204B is fixed in a state in which an annular rib 230, which is formed at the inner edge portion of the upper flange 204B, has entered into the reel hub 210. The braking member 220 is formed to have a diameter which is quite small as compared with the inner diameter of the reel hub 210, so that the braking member 220 can thereafter be inserted in and assembled into the reel hub 210 from the top end opening portion of the reel hub 210. Thus, the braking member 220 joggles within the reel hub 210. The standing ribs 228 are provided so as to eliminate such joggling.
In the recording tape cartridge, when the pressure by which the recording tape is wound the reel hub 210 is low, air or the like enters in between the layers of the recording tape. The frictional force between the layers decreases, which becomes a cause of offset between the layers (“steps” arise at the layers). These steps become a cause of the transverse direction end portions (edges) of the recording tape contacting the flanges or the like, or the recording surface being damaged by the edges of adjacent layers of the recording tape which have become offset, or the like. Thus, the pressure by which the recording tape is wound on the reel hub 210 must be set to be high.
However, in the conventional recording tape cartridge 200 such as that described above, the top end portion of the reel hub 210 is open. Thus, there are cases in which, in a vicinity of this open end of the reel hub 210, the strength with respect to the pressure of winding the recording tape is insufficient. In particular, a high-density recording tape requires an even higher pressure of winding onto the reel hub 210, and the problem of insufficient strength becomes marked.
Thus, the strength of the reel hub 210 has been improved by the material itself by mixing glass fibers into the resin material forming the reel 204. However, it is easy for glass fibers to damage the mold for molding the reel 204. Therefore, in consideration of the lifespan of the mold and the number of times the mold can be used while still in a good condition, the upper limit of the amount of glass fibers which can be included in the resin material is appropriately about 30%. There are limits to the improvement of the strength of reel hubs for high-density recording tapes, which reel hubs are formed so as to also include glass fibers.
Moreover, using the upper flange 204B to reinforce the vicinity of the open end of the reel hub 210 is not practical because this gives rise to deformation at the upper flange due to the pressure of winding, and causes wobbling of the surface of the reel 204.
A given effect of reinforcing the reel hub 210 is achieved by providing the standing ribs 228. However, the standing ribs 228 are thick portions of the reel hub 210 and are a cause of deterioration of the roundness of the reel hub 210. Thus, from this standpoint, it is preferable to not provide the standing ribs 228.
On the other hand, in order to achieve the effect of reinforcing the upper end portion of the reel hub 210 by the standing ribs 228, the standing ribs 228 must be provided up to a vicinity of the top end of the reel hub 210. However, in this case, when the reel rotates 204, it is necessary to prevent the standing ribs 228, which rotate integrally with the reel 204, and the braking member 220, which does not rotate, from interfering with each other. The clearance between the standing ribs 228 and the outer peripheral surface of the braking member 220 cannot be made sufficiently small. Thus, it is difficult to sufficiently suppress radial direction movement of the reel 204 with respect to the case 202 via the braking member 220.
Namely, it is difficult for the standing ribs 228 to sufficiently suppress radial direction movement of the reel 204 (i.e., for the standing ribs 228 to address the problems of a vertical-type drive device), while sufficiently reinforcing the reel hub 210.